The aim of this project is to define molecular events which control renin release. Renin is synthesized and stored in the granules of juxtaglomerular(JG) cells. It is the rate limiting enzyme for synthesis of angiotensin II (ang II), a potent vasoconstrictor hormone. The JG cells are modifed smooth muscle cells located primarily in the renal afferent arteriole adjacent to the glomerulus. The cellular basis for stimulus-secretion-coupling remains largely speculative, in part, because most studies have been impaired by an inability to isolate JG cell responses from other influential structures such as the macula densa and the sympathetic nervous system. We have recently isolated JG cells from whole kidneys and now propose to characterize the cells morphologically (using light and electron microscopic techniques), to establish conditions that influence renin release and to define factors which modify their phenotypic expression in tissue culture. Current evidence indicates that a rise in intracellular calcium inhibits renin release. It has been suggested that changes in the transmembrane potential of the JG cell control net influx and efflux of calcium. To date, there have been no measurements of transmembrane potential and intracellular calcium levels in association with renin release. We propose to characterize the electrophysiological properties of the isolated JG cell and to define the influence of the transmembrane potential and calcium on renin release. In addition to conventional techniques for intracellular recording, the voltage clamp technique using "patch electrodes" will be employed. Ang II inhibits renin release, and, in most effector organs, increases calcium permeability. There have been few attempts to characterize the angiotensin receptor on the JG cell. We propose, using radioligand techniques, to determine whether there is a heterogeneous or homogeneous population of Ang II receptors. We will establish, in a dose-dependent manner, angiotensin(and homologue) responses of JG cells in suspension and in culture. Using pharmacological and biochemical techniques, we will define the mechanism of action of angiotensin with emphasis on the role of guanylnucleotide regulatory proteins, modulation of adenylate cyclase and calcium activation of phosphodiesterase. Thus these studies will yield important new information on the mechanism responsible for the synthesis and release of renin and thereby factors which contribute to the production and maintenance of hypertension.